Damage metrics for masonry bridges under scour scenarios

Scour constitutes a significant treat to bridges. When it is not directly measured, it can be very difficult to detect and may go unnoticed until it produces catastrophic effects. Thus, understanding the effects of scour on bridge structures is of paramount importance for the development of effective scour monitoring strategies and early warning scour systems. This paper investigates the impact of scour on masonry arch bridges, which are the bridge typology most vulnerable to such a hazard. It aims at identifying synthetic damage parameters that can be used for bridge vulnerability and risk assessment, as well as at providing information about the optimal sensor placement in a monitoring system. For this purpose, extensive numerical analyses are performed on a representative bridge prototype to quantify how different response parameters, including kinematic parameters and modal parameters (i.e., the natural frequencies, and qualitatively the transverse mode-shapes), evolve under scour scenarios of increasing severity. The most recurrent damage scenarios involving piers, spandrel walls and arches are analysed to quantify the scour levels activating the various failure mechanisms, which can be finely detected and assessed through the numerical simulations. The study results allow identifying the parameters that are most sensitive to scour and the relevant limit values of interest for risk analysis. They are also useful to inform the development of optimal monitoring strategies for masonry arch bridges exposed to scour.